FIELD OF THE INVENTION
The invention relates to a configuration for folding sheets through the use of folding rolls and an adjustable stop.
Folding devices are needed for the preparation of sheets of letter paper to be inserted into envelopes or for the folding of sheets for bookbinding. Depending on the application, the sheets are to be folded simply in the middle if, for example, A4 format sheets are to be filled into C5 format envelopes, or are to be folded twice if, for example, A4 format sheets are to be filled into C6 format envelopes. In the latter case, the fold can be executed in a Z shape or as a so-called letter fold. If such folding devices are an integral part of sorting and enveloping devices, it is from time to time also necessary, for example in the case of account statements or bookkeeping documents, for the sheets to pass unfolded through the folding device.
Two folding principles have principally become widespread, namely the blade folding principle which is disclosed in German Published, Non-prosecuted Patent Application DE 40 18 709 A1 and German Patent DE 43 24 199 C1, and the buckle folding principle which is disclosed in German Patent DE 40 12 859 C2 and Published European Patent Applications 0 583 587 A1, 0 595 105 A1 and 0 641 733 A1.
In the case of the blade folding principle, the sheets to be folded are pressed through a gap between two folding rolls with the use of a sharp-edged blade which tapers to a point.
In the case of the folding device according to German Patent DE 43 24 199 C1, each folding roll is mounted in bearing levers which are adjustable about pivot axes. A folding roll gap is set through the use of a pivoting drive which engages on one bearing lever. The setting of the folding roll gap must be matched exactly to the thickness of the material to be folded, that is one or more sheets, and of the folding blade. Incorrect settings can lead to damage to the material to be folded or to folding errors. At each change of thickness of the material to be folded, the folding roll gap has to be adjusted anew. In order to achieve symmetrical pivoting of the oppositely disposed bearing levers, they have extensions which can be adjusted in relation to each other through the use of a compression screw and a fixing screw. The outlay for that folding device, in particular for the linear drive necessary for the first bearing lever and the adjustment, is correspondingly large.
In the case of the buckle folding principle, there are at least one pair of folding rolls and a folding pocket. The material to be folded is led between transport rolls and firstly into the folding pocket as far as a stop. The opening of the folding pocket, the folding pocket mouth, is located directly adjacent the folding region of the folding rolls. When the trailing end of the material to be folded is moved further by the transport rolls, a build-up occurs and the material to be folded bends in front of the folding pocket mouth into the folding region of the folding rolls, it is gripped by the latter and folded. In order to ensure that no curvature of the material to be folded occurs within the folding pocket, it must be narrow, corresponding to the thickness of the material to be folded, that is to say the play is closely limited. It is normally the case that one to five sheets can be folded simultaneously using the folding pocket method, if it is assumed that a sheet can weigh between 30 and 80 g. However, there is constantly the requirement to fold a larger number of sheets simultaneously.
A buckle folding machine which is known from Published European Patent Application 0 583 587 A1 has an adjustable stop rail in the folding pocket. In order to determine the folding length, corresponding to the penetration depth of the material to be folded into the folding pocket, and the folding shape, the stop rail can be set individually with the aid of an electric drive, and settings are carried out manually or through the use of a programmable control device. The stop rail has a plurality of stop fingers on that side facing the folding pocket mouth. The stop fingers have front end surfaces, lying on a common plane, which form the paper stop in the folding pocket. The stop rail can moreover assume a forward deflection position in which the front end surfaces jointly serve as a paper deflector and close the folding pocket mouth. The material to be folded and arriving at the folding pocket mouth is then deflected past the folding pocket, through the folding rolls, either to a following folding pocket or into an enveloping machine. In any case, by using that portion of the buckle folding machine, it is possible to realize both the "folding" function" and the "smooth passage" function, as mentioned at the outset. However, there are still problems with the folding width of the folding pocket.
Furthermore, a buckle folding machine which is known from Published European Patent Application 0 595 105 A1 has at least one folding pocket and folding rolls which can be set to different folding gap widths and can be moved pivotably and in a resilient or sprung manner with respect to each other. The folding rolls are rotatably mounted in two-armed pivoting lever pairs and, together with a further folding roll in each case, form a drawing-in and/or folding point. The inlet gap of the folding pocket has a minimum width and can be altered in a resilient manner according to the thickness of the material to be folded. The bottom and the top of the folding pocket are formed by grids which are pivotable about axes on the folding pocket base. The end sections on the inlet side of the grids are fastened on angle rails which run transversely to the filling direction and are coupled on the other side to the pivoting lever pairs of the folding rollers. Consequently, at the same time that the folding gap of the folding rolls is altered, the inlet gap of the folding pocket is adapted. However, the folding pocket in that way is normally of a wedge-shaped profile with a variable wedge width and the tip of the wedge being essentially of equal thickness. Therefore, the folding pocket mouth and the first two thirds of the folding pocket can be matched to the thickness of the material to be folded, but jamming at the folding pocket base is not thereby ruled out. An inlet barrier and an adjustable stop are not present in that buckle folding machine. Accordingly, it is only possible to process sheets of one length.
Finally, a further device for the folding of sheets or layers of sheet-like materials through the use of folding rolls is known from Published East German Patent Application DD-101 875, in which a pair of pressure rolls is disposed so as to be axially symmetrically adjustable in relation to the folding pair of rolls. The axial distance between the pressure rolls is smaller than that of the folding rolls. In that way, a folding blade can be dispensed with. All of the solutions mentioned above furthermore have the disadvantage of not being able to process sheets with a length smaller than the set folding length. However, sheets of that type are frequently contained as enclosures in mailings.